1. Field of the Invention
The invention relates to a method of molding an optical connector ferrule which is made of a resin.
2. Description of the Related Art
An optical connector in which plural optical fibers are fixed in parallel and guide pin holes are in parallel with them at their both sides is called an MT connector and widely used. An optical connector ferrule which is used in such an optical connector is molded by a transfer molding process using a thermosetting resin, or an injection molding process using a thermoplastic resin. In these processes, molding is basically conducted by interposing a core between upper and lower mold parts and injecting a resin into a cavity formed by the mold members.
FIGS. 6A and 6B show an example of a mold which is used in a molding process of the prior art. In the figure, FIG. 6A is a perspective view showing the state in which the mold is opened, and FIG. 6B is a front view showing the state in which the mold is set.
This example uses a core in which large-diameter guide pin hole forming pins 42, a tape fiber hole forming rectangular body 43, and a small-diameter optical fiber hole forming pins 41 are projected from a cavity block 44. The portions of the guide pin hole forming pins 42 and the optical fiber hole forming pins 41 which are close to the respective tip end portions are held by V-grooves 45b and 45a formed in a lower mold part 45, and fixed by fastening an upper mold part 46 to the lower mold part. In order to ensure precise alignment of optical fibers inserted into the optical fiber holes, the V-grooves 45b and 45a are precisely worked. In each of the optical fiber hole forming pins 41, the tip end portion has a reduced diameter and the rear portion 41a has a diameter which is larger than the reduced diameter.
A molding resin is injected into a cavity 49 which is formed around the guide pin hole forming pins 42, the tape fiber hole forming rectangular body 43, and the small-diameter optical fiber hole forming pins 41, and then cured. The upper and lower mold parts 46 and 45 are removed away and the resulting resin molded product is then pulled out from the core.
FIG. 7A is a perspective view of the resin molded product, and FIG. 7B is a section view of the resin molded product along the plane X--X' and Y--Y'. The resin molded product 50 has guide pin holes 51 and optical fiber holes 52. The diameter of each optical fiber hole is small in the tip end portion and increased in a middle portion. The optical fiber holes communicate with a taper fiber hole 54. The reference numeral 53 designates an opening through which an adhesive agent for fixation is supplied when a tape fiber wherein the covering of the tip end portion is removed away is inserted into the resin molded product, i.e., the optical connector ferrule. A projection 47 of the upper mold part 46 shown in FIGS. 6A and 6B is used for forming the opening. In FIG. 7A, the respective sizes are, for example, as follows:
The height of the resin molded product 50: 2.5 mm
The width of the resin molded product 50: 6.4 mm
The length of the resin molded product 50: 8 mm
The diameter of the optical fiber holes 52: 0.125 mm
The diameter of the guide pin holes 51: 0.7 mm
Since the large-diameter guide pin hole forming pins 42 and small-diameter optical fiber hole forming pins 41 which are attached to the core are held by the V-grooves 45b or 45a of the lower mold part 45 and a projection 48 of the upper mold part 46, there exist small spaces defined by the pins, the V-grooves, and the upper mold part. When a resin is injected into the cavity, therefore, the resin enters also these spaces. The entering resin must be removed away as chippings when the mold is opened and the resin molded product is taken out. If the removal is not perfectly conducted, the resin partly remains in the V-grooves. When the pins are set in the V-grooves for the next time, therefore, the pins are positionally deviated by the remaining resin, so that the alignment accuracy of the positions of the guide pin insertion holes and the optical fiber insertion holes is lowered.